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Page Title:
Additional Troubleshooting Tips on HVAC Equipment |
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 TM 55-1905-223-24-17
2-13. Additional Troubleshooting Tips on HVAC Equipment . The following information is furnished to
aid maintenance personnel when tracking down a problem with certain equipment in the HVAC subsystem.
a. Duct Heaters (DH).
(1) No Heat.
(a) Check to see that the controlling thermostat is set to call for HEATING. Check fan switch to
see that it is ON. If the fan runs, you have learned there is power to that section and that the
fan relay and motor are apparently operating properly. Return the fan switch to the AUTO
position and check the heater for the problem.
(b) Check and determine that power and proper voltage are going to the heater.
WARNING
Turn power OFF when checking continuity of components.
(c) With ALL HIGH VOLTAGE OFF, various components can be checked with an ohmmeter to
determine if they are defective.
(d) Replace defective parts, but note the following:
1
An open fusible link or manual reset is usually caused by a stuck contactor that allows a heater
to run on after thermostat is satisfied and the fan goes off.
(e) Use the exact part or approved alternates when replacing non-functioning parts.
(2) Not Enough Heat.
(a) If proper voltage is going to the heater and heater components are apparently operating
properly, use an ammeter and check the ampere draw of the heater. The amperage should be
no more than 10 percent lower than the full amp rating on the heater data plate.
(b) A heater that cycles off before the thermostat is satisfied may cause complaints only during the
coldest days when maximum performance is required.
(c) A thermostat with a defective heat anticipator or incorrect differential setting will short cycle a
heater OFF before the set temperature is reached and when maximum running time may be
required.
2-29
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